Recently, extreme ultra-violet (EUV) lithography has come to be used with the miniaturization of semiconductor devices. The wavelength of EUV light is as short as 13.5 nm and the light is instantly attenuated in air. Therefore, it is required to incorporate an exposure optical system in vacuum in a wafer exposure apparatus (EUV scanner) using EUV light. In this case, since a reticle stage itself is placed in vacuum, a vacuum chuck cannot be used for a chucking mechanism of an EUV mask and an electrostatic chucking system is used. In the electrostatic chucking system, a chucking region with a larger area is required to provide the same holding power in comparison with a vacuum chucking system. Therefore, in the EUV mask, it is necessary to use a large portion of the backside surface thereof as a chucking region.
Thus, in the EUV lithography, since a large portion of the backside surface thereof is used as the chucking region, a foreign matter tends to be present on the surface of the chucking mechanism. If a foreign matter is sandwiched between the chucking mechanism and the EUV mask, the EUV mask is deformed and strain occurs on the pattern surface. As a result, there occurs a problem that a pattern transferred onto the wafer is strained. Further, since the chucking mechanism is provided in the large vacuum chamber, it is necessary to set the pressure in the vacuum chamber back to atmospheric pressure and perform a cleaning operation in order to eliminate the foreign matter. In this case, the stop time of the EUV scanner becomes long and mainly causes the operability of the EUV scanner to be lowered.